It is the process itself. The process involves pressurizing tainted water and pumping it into the earth with the explicit purpose of undermining the stability of layers of rock. It is pumped out, and then refilled when the gas has been tapped. All of this increases earthquakes. All of it. Also, how else do you propose we dispose of the toxic sludge? Fracking is an environmental nightmare every step of the way, disposal is just the shit cherry on top of the shit sundae.